1. Field of the Invention
This invention relates to a pulse-code-modulation (hereafter abbreviated as PCM) schemed sound processor suited for use, for example, in TV game machines, personal computers, electronic music instruments, communication network information terminals, portable information devices, communication karaoke sets, intellectual educational toys, teaching aids and so on, and to a sound processing apparatus including such a sound processor.
2. Description of the Prior Art
In the conventional information processing apparatuses, such as the home-use TV game machines and personal computers, and electronic music instruments, there exist many ones using a sound processing apparatus in order to generate music and sound effects according to a progress of software or operation by the user.
Such a sound processing apparatus reproduces music by sequentially setting parameters to control a sound source while interpreting real-time score data having, on a time axis, information including interval, pronunciations, mute and tone effects of sound to be reproduced.
As one of these sound processing apparatuses, the PCM sound modules are broadly used to store, as PCM data, sound waveform data providing a basis for a music instrument or the like and convert the pitch thereof for reproduction according to a musical interval instructed.
For example, the PCM sound module used in the TV game machines such as Super Famicom (trademark) and PlayStation (trademark) are connected as a bus slave to a common bus having, as a bus master, a central processor unit (hereafter abbreviated as CPU) as a host. Note that in the present specification the resources provided on a side of receiving an addresses of the input/output control unit, etc. are termed as bus slaves whereas the resources on a side of issuing an address of a CPU, etc. are as bus masters. These PCM sound modules store sound processing programs in their own local ROMs (Read Only Memories) and score data, sound waveform data, echoing work area in the local RAMs (Random Access Memories).
Meanwhile, the PCM sound modules for personal computers, such as Sound Blaster 32/64 (trademark), are connected as bus slaves to a system bus (PCI bus, ISA bus, etc.) of a personal computer and store score data and data, such as sound waveform tables, in their own local ROMs or local RAMs.
In the PCM sound modules, there is a necessity for the bus master on the common bus, such as a host CPU, to previously transfer various kinds of data to the local RAM prior to reproducing sound.
The scheme, used in the PCM sound modules, requires a large capacity of a local memory, such as a local ROM or local RAM, to store various kinds of data. Besides this, there is a problem that the number of music instruments to be simultaneously reproduced, the length of PCM data to be stream-reproduced, etc. are restricted by the local memory capacity.
In the particular system as the above, the data within the local RAM can be rewritten during reproduction. This however requires the bus master, such as a host CPU or DMA controller, on the common bus to administer transfer of data, thus reducing the process performance for the entire system.
Furthermore, the conventional PCM sound modules use a digital multiplier circuit to multiply the sound data for providing envelope or echo effects. Thus, a large circuit scale is needed in implementing multiplication at high speed.
Also, the conventional PCM sound source apparatuses performs digital addition in order to conduct simultaneous reproduction for a plurality of channels. The simultaneous reproduction for a multiplicity of channels requires accurate digital adders and digital/analog converters, thus forming one factor of increasing the scale of a circuit.